The present invention relates to an apparatus for unloading material such as chips or the like from the bottom of a silo, comprising a conveyer screw which at its inner end is mounted in an annular frame, which is rotatable about the central axis of the silo and surrounds a central outlet opening, for swinging the screw along the bottom of the silo, said screw being also mounted for rotation about its longitudinal axis for conveyance of material to the outlet opening, the rotation of the screw being accomplished by a drive means arranged stationary independently of the rotating frame, the power transmission taking place via a transmission means rotatably mounted in the frame, the axis of said transmission means coinciding with said central axis.
From U.S. Pat. No. 3,050,201 there is known an unloading apparatus which comprises only one drive motor which is arranged stationary outside the parts which follow the swinging motion of the conveyer screw. This one motor gives the screw both its swinging and its rotating motion, the power transmission being effected through a drive shaft which extends centrally through the bottom of the silo. The disadvantage of such an apparatus is that the drive shaft must be mounted in a lip which extends into the outlet orifice of the silo. This entails that unloading apparatuses of this type cannot be utilized if the silo contains material such as chips or the like, as such a material will pile up on the lip and clog the outlet orifice.
In U.S. Pat. No. 3,391,809 there is disclosed an apparatus which will give the same unloading problems as described in connection with the abovementioned U.S. patent specification, as the framework which carries the rotating annular frame onto which the inner end of the conveyer screw is mounted, as well as the pipes leading to the hydraulic drive means on the frame, extend into the outlet orifice through which the material in the silo is discharged.
An apparatus according to the German accepted patent application Ser. No. 2,010,214 solves the problem of obtaining a free outlet orifice for the content of the silo, in that the bearing of the rotating frame extends around the outlet orifice, i.e. the outlet orifice and a subsequent outlet funnel are positioned inside the bearing, which is arranged at the periphery of the rotating frame. The advantages of an unobstructed outlet orifice is achieved by arranging all the drive motors on the rotating frame. However, an apparatus of this type suffers from the disadvantage that the rotating frame and thereby the screw cannot swing continuously in the same direction due to the cables for the current supply to the drive motors. The screw therefore has to sweep back and forth over the bottom of the silo, thus complicating the installation, since such a reciprocating movement requires additional control equipment. Besides, since the direction of rotation of the screw must always be the same, the feeding of the material by the screw will vary depending on whether the screw is swung back or forth. To obtain a continuous swinging movement of the screw in one direction collector ring means would be required, which means is very unfavourable in the circumstances under which the silo operates.